We studied how genetic variation in social traits, fitness, and fitness correlates can be maintained. Our approach was two-fold: we use observations we make on wild birds to generate hypotheses which we then test experimentally. Our group had two main research areas:

1) Many social traits have direct and often severe fitness consequences; yet these traits vary considerably, both, within and between individuals. Social interactions with conspecifics can influence physiology, own social behaviour and even reproductive success. We quantified the effect of the social environment in a wild population. We used long-term data from pedigreed populations of house-sparrows – a classic model species - to quantify genetic parameters such as heritability, genetic correlations and social, or indirect genetic effects. Additionally, we conducted experiments on captive sparrows to explore these effects. Finally, we used theoretical models to determine the soundness of our explanations.

2) Why do organisms age? This is one of the big, unsolved questions in biology, because it is unclear how a process that ultimately decreases fitness can persist evolutionarily, and why species do not evolve to live longer. Many theories have been put forward to explain from an evolutionary perspective why organisms change with age, but it is likely that many factors contribute to the phenomenon. One factor that can strongly affect selection pressure for longevity has, however, not received much attention: the transgenerational effects of senescence. It has been known for nearly a century that a parent’s age can affect her offspring’s, and even her grand-offspring’s fitness, but it is not clear how this affects population dynamics and the evolution of ageing and longevity. We studied the effects of parental and grand-parental age on their offspring’s lifespan, reproductive success, physiology and genetics in a wild and a captive population of house sparrows.